1. Field of the Invention
The present invention relates to a pendulum scroll saw and, in particular, to a compass saw having a lifting rod for securing a saw blade, an entrain member for reciprocating the lifting rod and a motor for pivoting the entrain member about a rational axis, the lifting rod having a guide surface connectable with the entrain member.
2. Description of the Prior Art
Pendulum scroll saws of the type described above find their application in cut-off processes. A saw blade is releasably attached to a lifting rod that performs a pendulumxe2x80x94like reciprocating movement. For transforming a rotational movement of a motor into pendulumxe2x80x94like reciprocating movement, the lifting rod is provided with a crank. In one of the reciprocating directions of the lifting rod, the saw blade performs a sawing stroke, cutting the material, and performs an idle stroke in the opposite direction. During the idle stroke, no cutting of the material, e.g., wood or plastic, takes place.
German Publication DE-128 19 527 discloses a pendulum scroll saw with a motor-driven lifting rod. At one of its end, the lifting rod is provided with a tool holder for receiving a blade of a compass saw and is provided at its opposite end with a flat section having a guide opening. An eccentrically rotatable entrain member is arranged in""the guide opening. The entrain member has a guide surface that contacts the lifting rod in particular the edge of the guide opening. The guide surface extends transverse to the reciprocating direction of the lifting rod and transverse to the rotational axis of the entrain member.
The advantage of the known solution consists in a constructively easy transformation of the circular movement of the entrain member in a linear movement. This provides for an economical manufacturing of the pendulum scroll saws.
The drawback of the known solution consists in that the linear movement has a sinusoidal speed gradient. The drawback of the sinusoidal speed gradient consists in that, on one hand, the saw blade has a variable sinusoidal speed and, on the other hand, the duration of the idle stroke corresponds to the duration of the sawing stroke. These two factors lead to an unsatisfactory sawing output of a pendulum scroll saw and to a prohibitive idle time.
Accordingly, an object of the present invention is to provide a pendulum scroll saw of the type described above and having a high sawing output and, which at the same time, can be economically manufactured.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a pendulum scroll saw of the type described above and in which the contact region of the guide surface with the entrain member has a curved profile that deviates from a straight line.
The deviation of the curved profile of the contact region of the guide surface with the entrain member from a straight line in a direction transverse to the reciprocating direction, permits, on one hand, to optimize the durations of the idle and sawing strokes and, on the other hand, to optimize the speed gradient, in particular, during the sawing stroke. The deviation of the contact region from a straight line, in a direction transverse to the reciprocating direction, permits to eliminate a sinusoidal speed gradient of the lifting rod and, thereby, of the saw blade.
The guide surface provides for displacement of the entrain member, during the sawing stroke, relative to the lifting rod, advantageously along a substantially rigid monotonous falling convex or rising concave curve. A so formed guide surface insures a high output capacity of the pendulum scroll saw. In addition, the duration of the idle stroke is smaller than that of the sawing stroke, which increases the service or useful time of the saw and the efficiency of the cutting process. During the idle stroke, advantageously, a guide surface, which has the same profile, is used. This insures an economical manufacture of the pendulum scroll saw.
In order to insure a uniform speed gradient, at least during the sawing stroke, the curved profile corresponds preferably to a polynom of nth degree. This profile of the guide surface provides for a substantially optimal and continuous speed gradient.
Advantageously, the curved profile corresponds to a polynom of second degree, which on one hand, insure a substantially uniform speed during the sawing stroke and, on the other hand, insure a simplest shape of the lifting rod.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and it mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.